The present invention relates generally to controlling the bypass clutch of a torque converter for an automotive vehicle.
A conventional automatic transmission includes a torque converter, located in the power path between an engine crankshaft and transmission input shaft. A torque converter includes a bladed impeller wheel driveably connected to the engine crankshaft, a bladed turbine wheel driveably connected to the transmission input shaft, a bladed stator wheel, and a toroidal chamber containing pressurized hydraulic fluid for producing a hydrokinetic connection between the impeller and turbine. The torque converter attenuates torque transients and vibrations, increases torque transmitted to the turbine from the impeller at low speed, and provides a smooth transition during gear ratio changes. Because of slippage between the input and output, the torque converter has a low operating efficiency.
Current automotive automatic transmissions use a converter bypass clutch to improve fuel economy primarily at highway vehicle speed. When the bypass clutch is fully engaged, it produces a mechanical drive connection between the impeller and turbine, thereby replacing the hydrokinetic drive connection. When the bypass clutch is fully disengaged, the mechanical drive connection is functionally replaced by the hydrokinetic drive connection. Usually a spring damper arranged in series with the bypass clutch is used to reduce engine torque fluctuation transmitted to the driveline. However, the bypass clutch, damper, control and strategy are usually not optimized to produce maximum fuel economy under city driving conditions.
There is a need for the torque converter, its bypass damper, bypass clutch, and control strategy to participate toward improving performance feel during certain transient conditions and to contribute more toward improvement in fuel economy under in city driving conditions. It is preferred that improved fuel economy and performance be realized without employing new automatic transmission architecture, such as the dual wet or dry input clutches used in powershift transmissions to replace and simulate the performance of the torque converter.